The Applicant has invented an ink jet printhead that is capable of generating text and images at a resolution of up to 1600 dpi.
In order to achieve this, the Applicant has made extensive use of micro electromechanical systems technology. In particular, the Applicant has developed integrated circuit fabrication techniques suitable for the manufacture of such printheads. The Applicant has filed a large number of patent applications in this field, many of which have now been allowed.
The printheads developed by the Applicant can include up to 84000 nozzle arrangements. Each nozzle arrangement has at least one moving component that serves to eject ink from a nozzle chamber. The components usually either act directly on the ink or act on a closure which serves to permit or inhibit the ejection of ink from the nozzle chamber.
The moving components within the printheads are microscopically dimensioned. This is necessary, given the large number of nozzle arrangements per printhead. The Applicant has spent a substantial amount of time and effort developing configurations for such printheads.
One of the reasons for this is that, as is known in the field of integrated circuit fabrication, cost of on-chip real estate is extremely high. Furthermore, it is important that levels of complexity are kept to a minimum since these significantly increase the cost of fabrication.
As a result of the need to keep on-chip real estate to a minimum, the Applicant has developed printhead chips that are extremely thin, having a high length to width ratio. These chips are positioned end-to-end to span a medium on which ink is to be deposited.
A substantial difficulty to be overcome with such printheads is the supply of ink to the nozzle arrangements. A possibility investigated by the Applicant was the provision of ink passages extending the length of the printhead chips, each passage carrying a different color. However, it will be appreciated by those of ordinary skill in the field of fluid mechanics that ink driven through such passages would be subject to an extremely high pressure drop. This pressure drop inhibits the ink from being carried at a suitably high flow rate. In FIG. 1 of the drawings, there is shown a printhead chip 1 incorporating three passages 2, one for each color, extending the length of the printhead chip. The problem associated with pressure drop in the passages is immediately apparent to a person of ordinary skill in the field of fluid mechanics, given the small cross sectional area of these passages.
An important requirement for the nozzle arrangements of this form of printhead is that they be refilled quickly once ink has been ejected from the nozzle chambers. This ensures that the nozzle arrangements can re-fire in a very short time, leading to rapid printing, which is an advantage sought by the Applicant. The high pressure drop mentioned in the previous paragraph inhibits the development of a suitable flow rate to the nozzle chambers and consequent rapid re-firing.
In order to address this issue, one example of a printhead chip has rows of ink inlet openings defined therein into which ink is fed. Each row of ink inlet openings corresponds to a differently colored ink. Thus, the necessity of having ink flowing lengthwise in each chip is obviated.
For color printing, at least three different inks must be provided to the printhead chip. These are Cyan, Magenta and Yellow inks. It is critical that these inks are kept separate from each other up to the point of impact on the print medium since the printhead chip prints a dithered image. It follows that it is necessary to provide each inlet opening with an ink of a different color. This is shown schematically in FIG. 2. As can be seen in FIG. 2, this can be achieved by providing a primary channel or reservoir 3 for each color. The ink from each reservoir 3 is fed into smaller channels 4, which in turn feed into the rows of ink inlet openings in a printhead chip 5.
It is to be appreciated that an ink distribution assembly comprising the reservoirs 3 and the smaller channels 4 must be manufactured with a high degree of accuracy due to the small size of the channels in the printhead chip 5 and the necessity for consistent ink flow to the openings in the printhead chip 5.
One way of achieving this accuracy would be to machine the assembly out of silicon. However, Applicant has found that this would result in a product that is far too costly to be commercially competitive.
It follows that the assembly should preferably be molded of a plastics material. The principle forms of molding plastics material are extrusion molding and injection molding. Applicant has found that extrusion molding is not capable of producing a product that has the required accuracy and structural stability for the assembly in question.
Substantial advances have been made in injection molding over the past years. Applicant has found that this form of molding can provide an assembly with the required accuracy and stability of construction. However, Applicant has identified a difficulty in injection molding an assembly having more than two reservoirs for ink. This is associated with the fact that it would appear that such a structure would require the construction of side mover cores when fabricating the molds to be used in the injection molding process. These cores are generally complex and expensive to manufacture. In FIG. 3, there is shown what would be an intuitive assembly including three ink reservoirs 6 molded in a plastics material, one for each ink of a particular color. It is clear that injection molding such an assembly would require the use of side mover cores.
The Applicant has thus developed a distribution assembly that obviates the need for such side mover cores in its fabrication.